The objective of this research program is to investigate the roles of cAMP, calcium, and hormones in the light- and circadian-regulation of teleost retinomotor movements. Retinomotor movements are produced by elongation and contraction of photoreceptors and migration of pigment granules within the RPE. They serve to position photoreceptors and screening pigment for optimal day or night vision. In constant darkness retinomotor movements persist; thus they appear to be regulated by circadian rhythm as well as light. We have shown that cAMP induces movements characteristic of darkness (night) in photoreceptors and RPE and that calcium is required for cone contraction. In this application we propose (1) to investigate the role of cAMP in promoting dark-adaptive retinomotor movements by examining dark- and cAMP-induced protein phosphorylation in RPE and in isolated photoreceptor fragments which contain inner and outer segments (IS/OS). The inner segments of these fragments are motile. (2) We will investigate the roles of calcium and calmodulin in regulating retinomotor movements by identifying calmodulin-binding proteins and examining calcium dependent protein phosphorylation in RPE and photoreceptor IS/OS. (3) We will investigate the effects of light on cAMP and cGMP levels in photoreceptor IS/OS by radioimmunoassay. (4) Finally we will examine the effects of hormones known to infuence cAMP levels on retinomotor movements in cultured retinas, on RPE and photoreceptor IS/OS cAMP levels, and on protein phosphorylation. We believe that information obtained from these studies will provide clues to the roles of these agents in regulating more general metabolic and physiological processes of photoreceptors and RPE in all species.